(Not Applicable)
This invention relates to transient voltage surge suppression (TVSS) between a conventional watt-hour meter location and a socket into which the meter""s electrical contactor blades ordinarily plug, especially indicators of circuitry operability or ready condition.
Electrical power that public or private utilities supply to users of electricity is susceptible to transient voltage variation attributable to lightning strikes and/or switching malfunctions. The desirability of protecting utility watt-hour meters and sensitive downstream electrical equipment from voltage surges is obvious. Customers traditionally bore the economic brunt of current surges, as light bulbs and motor windings failed (xe2x80x9cburned outxe2x80x9d) from time to time as a result. However, that is becoming even less acceptable in an age of solid-state electronic devices, which often may be damaged worse by smaller surges than burned out appliance motors and radios in the past. Electrical utilities are now having to exercise more quality control over their product, to render it merchantable for modern-day usesxe2x80x94or be liable for not doing so.
The utility industryxe2x80x94slowly but surelyxe2x80x94is realizing that the time has come to provide transient voltage surge suppression (TVSS), preferably in the vicinity of the usual watt-hour meter. Indeed, more forward-looking members of the utility industry are promoting surge protection, and the manufacturers of TVSS equipment are seeking suitable equipment to meet the need.
Conventional watt-hour meters are commonly interposed between an external power source and electrical equipment downstream so as to measure the amount of electrical energy or power utilized by the downstream equipment. Such meters have protruding bladelike contactors that plug into complementary socket jaws connected to power-line leads at a box or panel, as at a power customer""s location. Plug-and-jack circuit-interruption devices for use between such an electric meter and premises where downstream electrical loads are powered from external power lines and metered by such meter include over-current circuit-interrupting means (breaker switches, with or without associated fuses), as suggested by Megarian in U.S. Pat. No. 3,599,047 and by St. John in U.S. Pat. No. 2,606,232. Such devices were contained within an interposed housing, which has come to be known simply as a xe2x80x9cmeter adapter.xe2x80x9d The meter is unplugged from its socket in the customary box or panel; the adapter is then plugged into the socket; and finally the meter is plugged into the adapter.
Solid-state over-voltage protective devices are known, whose resistance varies non-linearly under applied voltage, so that their electrical conduction is minimal at normal power voltages but disproportionately greater at higher surge voltages. Such a device, connected between a power line lead and an available ground lead, can clip off surge voltages and shunt surge currents safely to ground. A class of such devices is known by the name xe2x80x9cvaristor.xe2x80x9d Varistors connected to suppress transient surges have been proposed for use in watt-hour meters, as in Melanson U.S. Pat. No. 3,914,657 and Zisa U.S. Pat. No. 3,725,745, but such a locale for surge suppression has not been adopted to any appreciable extent. A more popular location for use of varistors in surge suppression has been in plug-in devices between electrical wall outlets and appliances to be operated by electricity drawn from such outlets. An example is found in Dell Orfano U.S. Pat. No. 4,089,032.
Despite (or perhaps because of) the teachings of such patents, interposition of a varistor or similar over-voltage protective means between a watt-hour meter and the meter socket was not known or practiced, until after the present inventor did so in the mid-1980s. He has pioneered increased surge capacity and safety of TVSS apparatus by heat-sinking component varistors, as in his U.S. Pat. No. 4,931,895 (soon to issue); by inserting temperature-responsive or xe2x80x9cthermalxe2x80x9d fuses or like cutoff devices to sense temperature and to disconnect the varistors from the power lines to preclude failure from excessive temperature rise (as in his U.S. Pat. No. 4,866,560); by stacking varistor disks in parallel circuit therein (as in his U.S. Pat. No. 4,901,187); and by including distributed-resistance fuse linksxe2x80x94with and without thermal cutoff means and/or varistor stackingxe2x80x94between power line leads and such varistors (as in his U.S. Pat. No. 4,907,119).
In view of the extremexe2x80x94and extremely shortxe2x80x94voltage surges and the very large resulting surge currents, testing sites for apparatus of this general type have been rather limited (and testing costly) so that in most instances it is impracticable for users to test competing equipment or to verify (or disprove) operating specifications or technical claims of suppliers. Competing manufacturers may or may not have done such testing, but they have overwhelmingly adopted the meter adapter as the preferred means of carrying varistors connected in the vicinity of the watt-hour meter to provide TVSS.
As is true with any largely passive device, a simple method of ascertaining its operational condition is desirable, preferably one not requiring disassembly of the adapter and/or its contents. Known for this purpose in downstream individual TVSS plug-in devices, as in the above noted Dell orfano patent, are indicator lights actuated by the incoming powerxe2x80x94and thereby showing a state of readiness when on (lighted). Such lights are useful, although they may give an erroneous xe2x80x9coff-linexe2x80x9d signal after failing from whatever cause, despite continued operability of the surge-suppression circuitry it self.
A primary object of the present invention is to enable transient voltage surge suppression (TVSS) circuitry installed in the vicinity of watt-hour meters to be checked for operational readiness by visual observation.
Another object of this invention is to provide an indication of circuit continuity or discontinuity visible from outside a watt-hour meter adapter containing TVSS circuitry and interposed between the meter itself and its customary socket in a wall box or panel.
A further object is to provide positive visual indication that a TVSS meter adapter is either operative or inoperative.
In general, the objects of the present invention are attained by shunting transient surges in externally supplied electrical power to ground by way of a plug-and-jack meter-to-socket adapter having either (or preferably both) one or more indicator lights and/or a translucent window in the adapter housing wall.
Other objects of the present invention, together with means and methods for attaining the various objects, will be apparent from the description and the accompanying diagrams of specific embodiments, which are presented by way of example rather than limitation.